(i) Field of the invention
This invention generally relates to a data collecting system and more particularly to a system according to which portable data collectors are carried by the users to collect the data, and the data are transferred to a central processing unit so as to be processed and stored therein.
(ii) Description of the Prior Art
A conventional data collecting system consists of connecting portable data collectors directly to a central processing unit via a communication line, in order to transmit and receive the data.
In the conventional data collecting system, however, the portable data collectors are provided with an interface circuit that connects to the host computer. Further, the interfaces that connect to the central processing unit require an interface circuit or a connector that meets the ratings such s EIA RS 232C or RS 422, making it difficult to reduce the size and weight or to make the device moisture-proof. Moreover, the data collectors are used at all times being powered by a cell. To restrain the consumption of current by the circuits, therefore, it is not feasible to use clock signals of a high frequency, and the transmission speed of the interfaces is 9600 bps at the greatest. Furthermore, the connector which is attached and detached repetitively loses its reliability. Moreover, since the data are transferred in a one-to-one manner between the portable data collector and the host computer, one of the portable data collectors occupies the central processing unit, and other portable data collectors must wait for their turns. Therefore, the efficiency of data transfer is very poor.
Even if the host computer transfers the same data which requires a long time for transferring to a plurality of portable data collectors, the central processing unit has to transfer the data to each portable data collector sequentially, and so it causes a waste of time.